Most industrial gas turbines have an automatic fuel shut-off system to stop fuel flow to the combustor(s) of the gas turbine. Such automatic fuel shut-off systems stop fuel flow when an emergency or abnormal operating condition is detected in the gas turbine. The automatic fuel shut-off system is also used to close an inactive fuel supply in favor of an active fuel supply, when the gas turbine has dual-fuel supplies. A common automatic fuel shutoff system is a trip oil system that hydraulically controls the fuel shut-off valves for a gas turbine. The current invention relates to improvements to a trip oil system.
The fuel shut-off valves of an industrial gas turbine typically are biased closed to prevent fuel flow unless an actuating force is applied to the valve. This actuating force is provided by the hydraulic fluid pressure supplied by a trip oil system. During start-up and operation of the gas turbine, trip oil systems apply hydraulic fluid to actuate and hold open fuel shut-off valves so that fuel flows to the combustors of the gas turbine. The trip oil systems relieve hydraulic pressure to allow the shut-off valves to isolate an unused fuel supply in a dual fuel supply system or stop fuel flow altogether if certain problems are detected in the gas turbine. Such failures and problems can include an overspeeding turbine, flame-out or abnormal turbine temperature.
Trip oil systems must operate reliably and consistently to ensure the uninterrupted normal operation of an industrial gas turbine. Fuel flows to an industrial gas turbine only if a fuel shut off valve is held open by the trip oil system. If the hydraulic pressure from the trip oil system needed to hold open a fuel shut-off valve is not being applied because the trip oil system becomes inoperative or because the trip oil system needs to be tested or requires maintenance, then the fuel shut-off valve closes and the gas turbine stops. Stopping a gas turbine because of a malfunction, testing or maintenance of the trip oil system is a highly undesirable feature of prior art trip oil systems. In prior art trip oil systems, the failure, testing or maintenance of a single trip oil valve causes a fuel shut-off valve to close and stop an industrial gas turbine. Such interruptions in the operation of an industrial gas turbine are highly undesirable, and have been a long-term problem with prior trip oil systems. For example, FIG. 3 shows a prior art trip oil system having a single individual trip oil valve 90 for each branch of the trip oil conduits. If this one trip oil valve fails or requires service, then the associated fuel shut-off valve 92 stops the fuel flow to the combustor.
There has been long-felt need for an improved trip oil system that is extremely reliable, and can be tested and serviced while the gas turbine is operating. Prior trip oil systems have not satisfied this need. The current invention is an improved trip oil system that can be tested and serviced without interrupting operation of the gas turbine. One feature of the invention is that redundant trip oil valves have been substituted for the single, isolated valves of prior systems. Similarly, the current invention includes redundant components so that a failure in any one trip oil valve will not result in fuel shut-off to an industrial gas turbine, thereby causing the gas turbine to shut down.
Even worse, if the single trip valve of the prior art system does not react to a signal from a controller 94 to shut off the fuel flow then fuel will continue to flow to the gas turbine and the continued operation of the gas turbine could cause damage. To detect a defective trip oil signal, it is known to employ redundant pressure sensors 96 to notify the controller 94 that the trip oil valve relieved pressure in its respective branch of the trip oil conduit system. If the controller is notified by two out of three pressure sensors that the trip oil pressure is high after the trip oil valve has been commanded to relieve pressure, then the controller acts to shut off the gas turbine. If only one pressure sensor indicates that the pressure is still high, a fault signal is generated by the controller to signal a defect, probably in the pressure sensor, in the trip oil system.